Innocent one in place for congregation (5)
I believe the answer is:
naive
'innocent' is the definition.
('naive' can be similar in meaning to 'innocent')
'one in place for congregation' is the wordplay.
'one' becomes 'i' (Roman numeral).
'in' is an insertion indicator.
'place for congregation' becomes 'nave' (part of a church).
'i' placed into 'nave' is 'NAIVE'.
(Other definitions for naive that I've seen before include "Too simple and trusting" , "Jejune" , "Lacking sophistication" , "Unsophisticated and gullible" , "Too trusting and impractical" .)